P CODES (POWERTRAIN) P0100 - P0199 P0139

    Definition of Trouble Code P0139 - Oxygen Sensor Circuit Slow Response (Bank 1 Sensor 2)

    Trouble code P0139 is triggered when the Engine Control Module (ECM) detects a slow response in the oxygen sensor's voltage, specifically in Bank 1 Sensor 2. This sensor is responsible for monitoring the level of oxygen in the exhaust gases and helps the ECM adjust the air-fuel mixture for optimal engine performance and emissions.

    How to Diagnose Trouble Code P0139

    Follow these steps to diagnose the P0139 trouble code:

    Step 1: Verify the code

    Use an OBD-II scanner to read the trouble codes stored in the ECM. Clear the codes, start the engine, and check if the P0139 code reappears. If it does, proceed to the next step.

    Step 2: Inspect the oxygen sensor and wiring

    Visually inspect Bank 1 Sensor 2 oxygen sensor and its wiring for any signs of damage, corrosion, or disconnection. If any issues are found, repair or replace the damaged components.

    Step 3: Check for exhaust leaks

    Exhaust leaks near the oxygen sensor can cause inaccurate readings, leading to a slow response. Inspect the exhaust system for any leaks and repair them as necessary.

    Step 4: Test the oxygen sensor

    Using a digital multimeter, test the oxygen sensor's voltage output while the engine is running. The voltage should fluctuate between 0.1V and 0.9V. If the voltage is outside this range or slow to respond, replace the oxygen sensor.

    Step 5: Test the ECM

    If the oxygen sensor and its wiring are in good condition, and there are no exhaust leaks, the ECM may be faulty. Consult a professional mechanic to verify the ECM's functionality and replace it if necessary.

    How to Repair Trouble Code P0139

    After diagnosing the cause of the P0139 code, follow these steps to repair the issue:

    Step 1: Repair or replace the oxygen sensor

    If the oxygen sensor is found to be faulty, replace it with a new one. Make sure to use an OEM-quality sensor to ensure accurate readings and proper function.

    Step 2: Repair or replace damaged wiring or connectors

    If any damaged wiring or connectors were found during the diagnosis, repair or replace them to ensure proper electrical connections.

    Step 3: Repair exhaust leaks

    If any exhaust leaks were found, repair them to prevent inaccurate oxygen sensor readings and ensure optimal engine performance.

    Step 4: Replace the ECM

    If the ECM is found to be faulty, replace it with a new or remanufactured unit. Consult a professional mechanic for proper installation and reprogramming.


    Trouble code P0139 - Oxygen Sensor Circuit Slow Response (Bank 1 Sensor 2) is a common issue that can be resolved by following the steps provided above. Ensure proper diagnosis and repair to maintain optimal engine performance and emissions control. If you are unsure about any steps or need professional assistance, consult a qualified mechanic to address the issue.

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